1. Field of the Invention
The present invention relates to a method of manufacturing an aluminum solid electrolyte capacitor whereby a product of high reliability can be mass-produced.
2. Description of the Related Art
In the aluminum electrolytic capacitors which are generally employed in large quantity, the positive electrode foil is constituted by etching aluminum foil to increase its surface area and generating an oxide film thereon by subjecting this to chemical conversion treatment; for the negative electrode foil, untreated aluminum foil is employed and an element (hereinbelow termed xe2x80x9ccoiled elementxe2x80x9d) is constituted by coiling the positive electrode foil and negative electrode foil with a separator such as Manila paper therebetween; the element is completed by impregnating with liquid electrolyte (for the essentials, see Laid-open Japanese Patent Application Publication No. H. 8-78287).
In recent years, aluminum solid electrolyte capacitors have been commercialized in which a conductive polymer material is employed as electrolyte instead of the liquid electrolyte in an aluminum electrolytic capacitor as aforesaid.
The solid electrolyte in an aluminum solid electrolyte capacitor has the characteristic advantage that its electrical conductivity is higher than that of the liquid electrolyte in an aluminum electrolytic capacitor, so losses are smaller and the frequency characteristic and temperature characteristics are excellent.
However, in contrast to aluminum electrolytic capacitors, the oxide film on the positive electrode has no self-repairing action, so if a defect is produced in the oxide film on the positive electrode, there is a high probability of a short-circuit mode fault being produced.
Usually, when a short-circuit occurs in a capacitor employed in electrical equipment, an abnormal current flows; this involves a risk of causing a fire in the electronic equipment. Accordingly, in the case of aluminum solid electrolyte capacitors, capacitors are employed in which the voltage-withstanding ability of the oxide film on the positive electrode is set to be about three times higher than in an aluminum electrolytic capacitors, but this causes the capacity to be reduced to about ⅓.
Apart from this problem, when an aluminum solid electrolyte capacitor is manufactured by applying the prior art (see for example Laid-open Japanese Patent Application Publication No. H. 10-50558 or Laid-open Japanese Patent Application Publication No. H. 10-50560), the oxide film on the positive electrode is subjected to a chemical conversion treatment again (xe2x80x9crepeat chemical conversionxe2x80x9d treatment) after the coiled element is produced, and before it is incorporated and fixed in the case.
FIG. 7 is a flow chart given in explanation of the steps involved in manufacturing a prior art aluminum solid electrolyte capacitor. First of all, in a first step, a coiled element is produced comprising a positive electrode foil formed with an oxide film by chemical conversion, a separator, and a negative electrode foil; in a second step, the oxide film of the positive electrode foil is subjected to repeat chemical conversion to repair any defects; in a third step, it is subjected to washing; in a fourth step, heat treatment is performed; in a fifth step, a solid electrolyte is generated; in a sixth step, this is assembled into the case; in a seventh step, the coiled element and case are stuck together by epoxy resin and curing is performed; in an eighth step, ageing is performed; and in a ninth step inspection is carried out.
In the process of FIG. 7 mentioned above, there is the problem that, even if the oxide film on the positive electrode is perfectly formed by the repeat conversion of the second step, if any kind of stress acts on the coiled element during the period from the subsequent third step to the seventh step i.e. from the washing as far as the incorporation in the case, cracks can easily be generated in the oxide film on the positive electrode.
Specifically, when the coiled element is incorporated in the case, until adhesion and curing of the epoxy resin have been achieved, the lead terminals of the coiled element can move easily and also the coiled element itself is weak and easily deformed by external force, so handling in such a way that no stress acts on the electrode foil is difficult to achieve and furthermore the oxide film on the positive electrode is as extremely thin as 1.3 (nm/V), so even if the utmost care is taken in each step, the defect rate is high and may reach 5 (%) to 50 (%); thus the reliability is low.
According to the present invention, a sequence of steps is adopted that makes it possible to avoid application of stress to the capacitor body (for example coiled element) when manufacturing an aluminum solid electrolyte capacitor and there are provided means that make it possible to execute these steps, thereby enabling mass production of aluminum solid electrolyte capacitors of high reliability and excellent quality.
The basis of the present invention lies in that, at the stage where the capacitor body for the aluminum solid electrolyte capacitor is completed, its assembling into the case is immediately performed, together with curing and adhesion with resin, thereby fixing the coiled element at the initial stage of the steps and preventing stress from being applied to the oxide film on the positive electrode; in order to perform such a step, a case is required having an aperture that makes possible performance of the various processing steps after curing and adhesion of the resin around the lead terminals in the coiled element; such a case is disclosed in Japanese Patent Application Number H. 7-135116 (Laid-open Japanese Patent Application Number H. 8-78287).
FIG. 1 is a flow chart given in explanation of an example of the steps involved in manufacturing an aluminum solid electrolyte capacitor according to the present invention. In the first step, a coiled element comprising a positive electrode foil with oxide film formed thereon by chemical conversion, a separator and an electrode foil is produced; in the second step, the coiled element is assembled through the first aperture in a case having a first aperture and a second aperture; in the third step, adhesion of the coiled element and the case is effected at the first aperture with an epoxy resin, followed by its curing; in the fourth step, defects are repaired by repeat chemical conversion of the oxide film of the positive electrode foil; in the fifth step, washing is performed; in the sixth step, heat treatment is carried out; in the seventh step the solid electrolyte is generated; in the eighth step ageing is performed; in the ninth step the second aperture is sealed; and the product is completed by inspection in the tenth step. The chief varieties of aluminum solid electrolyte capacitors are capacitors in which a coiled element is employed as described above and capacitors in which the electrodes are of a flat plate shape; including these cases, parts which are present in the case are collectively called the xe2x80x9ccapacitor bodyxe2x80x9d; in this construction, a portion of the lead terminals is also included in the xe2x80x9ccapacitor bodyxe2x80x9d.
As described above, according to a first aspect of the present invention, a method of manufacturing an aluminum solid electrolyte capacitor comprises:
a step of fixing a capacitor body (for example capacitor body 1 of FIG. 2, to be described) within a case (for example case 3 of FIG. 2, to be described) having one or more apertures; and
a step of generating solid electrolyte by introducing a raw material of solid electrolyte from any of these apertures, coating or impregnating the capacitor body therewith, and inducing an oxidative polymerization reaction.
The aforesaid one or more apertures can be employed as introduction ports when the capacitor body is arranged within the case. If this is done, it is important that the aperture is of a size that is capable of allowing passage of the capacitor body. However, this is not necessary if the capacitor body is arranged within the case by some other methods.
Other roles possessed by the one or more apertures referred to above comprise the role of a port through which air or a gas is evacuated from the interior of the case and the role of being employed as entry ports when the various liquids, described below, are introduced into the case. In this case, the apertures may be small so long as evacuation from within the case is possible and introduction of liquid into the case is feasible. A plurality of such apertures may be provided. The locations where these are arranged are not restricted to the end of the case as shown in FIG. 2, to be described, but could also be the side of the case.
In the above description, xe2x80x9cfixingxe2x80x9d means that the capacitor body is made unable to move freely within the case. Regarding the material employed for this fixing, any material may be employed so long as it is non-conductive; various types of resin product may be employed.
In particular, application of liquid resin followed by its solidification so as to fix the capacitor body and to seal the capacitor body in a way that the interior of the case is divided into two zones by solidification, is useful when introducing liquid utilizing pressure difference, as will next be described.
Preferably, in this case, a capacitor body is inserted into a case from one of said one or more apertures (in the specification of this application, this will be called the first aperture, for example first aperture 3A of FIG. 2, to be described), and
in the step of fixing the capacitor body, sealing is effected together with the fixing;
the interior of said case is evacuated, and
said raw material of solid electrolyte is introduced into this case that has been evacuated through an aperture (in the specification of this application, this will be called the second aperture, for example second aperture 3B of FIG. 2, to be described) other than the first aperture of said one or more apertures, by utilizing the difference in pressure with outside. This second aperture corresponds to an aperture for liquid introduction, of the one or more apertures mentioned above.
In this way, for example the benefit is obtained that deposition of the raw material of solid electrolyte on the case is reduced to the minimum, thereby enabling the load of subsequent cleaning to be reduced and also the benefit is obtained that the tendency for coating/impregnation of the raw material of the solid electrolyte into the interior of the capacitor body to be obstructed by the presence of air bubbles, etc. can be reduced, thereby making it possible to achieve reliable coating/impregnation.
Regarding the location of provision of the first aperture, provision of a wide aperture at one end of the case, such as 3A of FIG. 2, to be described, is preferable in that it facilitates insertion of the capacitor body.
Regarding the location of provision of the second aperture i.e. the aperture for introduction of liquid, preferably, this is provided in constricted form at the end on the opposite side to first aperture 3A, as 3B in FIG. 2, to be described. When manufacturing an aluminum solid electrolyte capacitor according to the invention of the present application, an operation is necessary of inverting the case in a condition with the liquid that has been introduced still present in the interior of the case; the constricted form of the aperture helps to easily prevent the liquid from overflowing. It is also desirable to provide a collar portion such as 3C in FIG. 2, to be described, at the aperture for liquid introduction. This is because, depending on the material of the case, final sealing of the aperture can easily be carried out by heat-welding this collar portion.
For the aforesaid fixing and sealing, any material may be employed so long as it conforms to the gist of the present invention. Specifically, conveniently, resin is employed that has fluidity and that loses this fluidity on subsequent solidification.
Taking into account the heat-resistance and the degree of non-fluidity of solidified resin, a hardening type resin is preferable. For example, epoxy resin, phenol resin, silicone resin, fluororesin, polyimide resin or modified forms of these can be employed. Of these, epoxy resin is particularly preferable from the point of view of diversity of properties and reliability etc.
When a hardening type resin such as epoxy resin is employed, in order to realize the aforementioned fixing/sealing, it is frequently necessary to arrange to dam (i.e. obstruct) the flow of the liquid sealant by inserting a solid plate (termed a sealant blocking member in this application) beforehand. It is also possible to give such a sealant blocking member a fixing function.
It should be noted that, although, in the present application, the resin for fixing or sealing is termed a sealant, this is not meant to imply that its application is restricted to sealing; use solely with the objective of fixing is also included.
Preferably in an aluminum solid electrolyte capacitor according to the present invention, a gap is provided between the capacitor body and the second aperture. This is because if such a gap is not ensured, the capacitor body blocks the aperture for liquid introduction. For this purpose, apart from suitably selecting the position of fixing or sealing of the capacitor body, it is effective to provide a projection in the interior of the case, as will be described.
Also, preferably, after the capacitor body has been coated or impregnated with the raw material of solid electrolyte, oxidizing agent for inducing an oxidative polymerization reaction of the raw material of solid electrolyte is introduced through the second aperture. Usually, if the oxidizing agent is co-present, the oxidative polymerization reaction according to the present invention will gradually proceed even at low temperature. Accordingly, it is desirable to mix the raw material of solid electrolyte and oxidizing agent and introduce this mixture into the case immediately thereafter. However, it has been discovered that there are no problems if, instead of doing this, after previously coating or impregnating the capacitor body with raw material of solid electrolyte, oxidizing agent for inducing the oxidative polymerization reaction of the solid electrolyte is introduced through the second aperture. It is thought that this is because, even in this way, contact of the raw material of solid electrolyte and the oxidizing agent can be achieved, sufficiently.
Preferably the raw material of solid electrolyte is 3,4-ethylenedioxy-thiophene.
Also, it is desirable to perform ageing during drying in a condition with the second aperture open after generation of the solid electrolyte by the oxidative polymerization reaction, or, after sealing and fixing of the capacitor body by epoxy resin in the interior of the case, prior to introduction of the raw material of solid electrolyte, to perform chemical conversion treatment by introducing chemical conversion liquid through the second aperture and passing current to the positive electrode, followed by washing and drying.
In addition, it is desirable to get rid of at least oxidizing agent present in the vicinity of the second aperture after introduction of the oxidizing agent.
Furthermore, when the raw material of solid electrolyte is introduced into the case, when the raw material and oxidizing agent are introduced, when other liquids such as washing liquid are introduced, during the chemical conversion treatment, during the ageing, etc., it is desirable to apply ultrasonic vibration. It is believed that this assists in removal of air bubbles, mixing of liquids, reduction of dead space, and in reaction promotion, etc. In particular, it is desirable to apply ultrasonic vibration when the raw material of solid electrolyte and oxidizing agent are introduced and during chemical conversion treatment or during ageing.
In the washing step, preferably washing is effected by immersing the second aperture in the tank that holds the washing liquid, followed by repeated pressure reduction and pressurization of the interior of the tank to cause inflow of the washing liquid into the case and its outflow from the case.
A further aspect of the present invention consists in:
an aluminum solid electrolyte capacitor component comprising:
a capacitor body;
a case in which this capacitor body is accommodated;
a sealant layer that fixes this capacitor body within this case and divides the interior of this case into two zones;
a sealant blocking member for arranging that this sealant does not penetrate into one of these zones of the case;
and an aperture provided in the zone in which it is arranged that this sealant does not penetrate, and
an aluminum solid electrolyte capacitor manufactured from such a component.
As described in the above, since the capacitor body is protected from external force by being within the highly rigid case from the very beginning, even if handling is somewhat rough, there is no risk of defects being produced by application of stress to the oxide film on the positive electrode, so an aluminum solid electrolyte capacitor of high reliability can be realized.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings and the table.